summaryrefslogtreecommitdiffstats
path: root/drivers/xen/gntdev.c
blob: c77a0751a31173344de0c02c3f70d18ec259ca63 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
/******************************************************************************
 * gntdev.c
 *
 * Device for accessing (in user-space) pages that have been granted by other
 * domains.
 *
 * Copyright (c) 2006-2007, D G Murray.
 *           (c) 2009 Gerd Hoffmann <kraxel@redhat.com>
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#undef DEBUG

#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/mmu_notifier.h>
#include <linux/types.h>
#include <linux/uaccess.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/highmem.h>

#include <xen/xen.h>
#include <xen/grant_table.h>
#include <xen/balloon.h>
#include <xen/gntdev.h>
#include <xen/events.h>
#include <xen/page.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Derek G. Murray <Derek.Murray@cl.cam.ac.uk>, "
	      "Gerd Hoffmann <kraxel@redhat.com>");
MODULE_DESCRIPTION("User-space granted page access driver");

static int limit = 1024*1024;
module_param(limit, int, 0644);
MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped by "
		"the gntdev device");

static atomic_t pages_mapped = ATOMIC_INIT(0);

static int use_ptemod;
#define populate_freeable_maps use_ptemod

struct gntdev_priv {
	/* maps with visible offsets in the file descriptor */
	struct list_head maps;
	/* maps that are not visible; will be freed on munmap.
	 * Only populated if populate_freeable_maps == 1 */
	struct list_head freeable_maps;
	/* lock protects maps and freeable_maps */
	struct mutex lock;
	struct mm_struct *mm;
	struct mmu_notifier mn;
};

struct unmap_notify {
	int flags;
	/* Address relative to the start of the grant_map */
	int addr;
	int event;
};

struct grant_map {
	struct list_head next;
	struct vm_area_struct *vma;
	int index;
	int count;
	int flags;
	atomic_t users;
	struct unmap_notify notify;
	struct ioctl_gntdev_grant_ref *grants;
	struct gnttab_map_grant_ref   *map_ops;
	struct gnttab_unmap_grant_ref *unmap_ops;
	struct gnttab_map_grant_ref   *kmap_ops;
	struct gnttab_unmap_grant_ref *kunmap_ops;
	struct page **pages;
	unsigned long pages_vm_start;
};

static int unmap_grant_pages(struct grant_map *map, int offset, int pages);

/* ------------------------------------------------------------------ */

static void gntdev_print_maps(struct gntdev_priv *priv,
			      char *text, int text_index)
{
#ifdef DEBUG
	struct grant_map *map;

	pr_debug("%s: maps list (priv %p)\n", __func__, priv);
	list_for_each_entry(map, &priv->maps, next)
		pr_debug("  index %2d, count %2d %s\n",
		       map->index, map->count,
		       map->index == text_index && text ? text : "");
#endif
}

static void gntdev_free_map(struct grant_map *map)
{
	if (map == NULL)
		return;

	if (map->pages)
		gnttab_free_pages(map->count, map->pages);
	kfree(map->pages);
	kfree(map->grants);
	kfree(map->map_ops);
	kfree(map->unmap_ops);
	kfree(map->kmap_ops);
	kfree(map->kunmap_ops);
	kfree(map);
}

static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
{
	struct grant_map *add;
	int i;

	add = kzalloc(sizeof(struct grant_map), GFP_KERNEL);
	if (NULL == add)
		return NULL;

	add->grants    = kcalloc(count, sizeof(add->grants[0]), GFP_KERNEL);
	add->map_ops   = kcalloc(count, sizeof(add->map_ops[0]), GFP_KERNEL);
	add->unmap_ops = kcalloc(count, sizeof(add->unmap_ops[0]), GFP_KERNEL);
	add->kmap_ops  = kcalloc(count, sizeof(add->kmap_ops[0]), GFP_KERNEL);
	add->kunmap_ops = kcalloc(count, sizeof(add->kunmap_ops[0]), GFP_KERNEL);
	add->pages     = kcalloc(count, sizeof(add->pages[0]), GFP_KERNEL);
	if (NULL == add->grants    ||
	    NULL == add->map_ops   ||
	    NULL == add->unmap_ops ||
	    NULL == add->kmap_ops  ||
	    NULL == add->kunmap_ops ||
	    NULL == add->pages)
		goto err;

	if (gnttab_alloc_pages(count, add->pages))
		goto err;

	for (i = 0; i < count; i++) {
		add->map_ops[i].handle = -1;
		add->unmap_ops[i].handle = -1;
		add->kmap_ops[i].handle = -1;
		add->kunmap_ops[i].handle = -1;
	}

	add->index = 0;
	add->count = count;
	atomic_set(&add->users, 1);

	return add;

err:
	gntdev_free_map(add);
	return NULL;
}

static void gntdev_add_map(struct gntdev_priv *priv, struct grant_map *add)
{
	struct grant_map *map;

	list_for_each_entry(map, &priv->maps, next) {
		if (add->index + add->count < map->index) {
			list_add_tail(&add->next, &map->next);
			goto done;
		}
		add->index = map->index + map->count;
	}
	list_add_tail(&add->next, &priv->maps);

done:
	gntdev_print_maps(priv, "[new]", add->index);
}

static struct grant_map *gntdev_find_map_index(struct gntdev_priv *priv,
		int index, int count)
{
	struct grant_map *map;

	list_for_each_entry(map, &priv->maps, next) {
		if (map->index != index)
			continue;
		if (count && map->count != count)
			continue;
		return map;
	}
	return NULL;
}

static void gntdev_put_map(struct gntdev_priv *priv, struct grant_map *map)
{
	if (!map)
		return;

	if (!atomic_dec_and_test(&map->users))
		return;

	atomic_sub(map->count, &pages_mapped);

	if (map->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
		notify_remote_via_evtchn(map->notify.event);
		evtchn_put(map->notify.event);
	}

	if (populate_freeable_maps && priv) {
		mutex_lock(&priv->lock);
		list_del(&map->next);
		mutex_unlock(&priv->lock);
	}

	if (map->pages && !use_ptemod)
		unmap_grant_pages(map, 0, map->count);
	gntdev_free_map(map);
}

/* ------------------------------------------------------------------ */

static int find_grant_ptes(pte_t *pte, pgtable_t token,
		unsigned long addr, void *data)
{
	struct grant_map *map = data;
	unsigned int pgnr = (addr - map->vma->vm_start) >> PAGE_SHIFT;
	int flags = map->flags | GNTMAP_application_map | GNTMAP_contains_pte;
	u64 pte_maddr;

	BUG_ON(pgnr >= map->count);
	pte_maddr = arbitrary_virt_to_machine(pte).maddr;

	/*
	 * Set the PTE as special to force get_user_pages_fast() fall
	 * back to the slow path.  If this is not supported as part of
	 * the grant map, it will be done afterwards.
	 */
	if (xen_feature(XENFEAT_gnttab_map_avail_bits))
		flags |= (1 << _GNTMAP_guest_avail0);

	gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, flags,
			  map->grants[pgnr].ref,
			  map->grants[pgnr].domid);
	gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr, flags,
			    -1 /* handle */);
	return 0;
}

#ifdef CONFIG_X86
static int set_grant_ptes_as_special(pte_t *pte, pgtable_t token,
				     unsigned long addr, void *data)
{
	set_pte_at(current->mm, addr, pte, pte_mkspecial(*pte));
	return 0;
}
#endif

static int map_grant_pages(struct grant_map *map)
{
	int i, err = 0;

	if (!use_ptemod) {
		/* Note: it could already be mapped */
		if (map->map_ops[0].handle != -1)
			return 0;
		for (i = 0; i < map->count; i++) {
			unsigned long addr = (unsigned long)
				pfn_to_kaddr(page_to_pfn(map->pages[i]));
			gnttab_set_map_op(&map->map_ops[i], addr, map->flags,
				map->grants[i].ref,
				map->grants[i].domid);
			gnttab_set_unmap_op(&map->unmap_ops[i], addr,
				map->flags, -1 /* handle */);
		}
	} else {
		/*
		 * Setup the map_ops corresponding to the pte entries pointing
		 * to the kernel linear addresses of the struct pages.
		 * These ptes are completely different from the user ptes dealt
		 * with find_grant_ptes.
		 */
		for (i = 0; i < map->count; i++) {
			unsigned long address = (unsigned long)
				pfn_to_kaddr(page_to_pfn(map->pages[i]));
			BUG_ON(PageHighMem(map->pages[i]));

			gnttab_set_map_op(&map->kmap_ops[i], address,
				map->flags | GNTMAP_host_map,
				map->grants[i].ref,
				map->grants[i].domid);
			gnttab_set_unmap_op(&map->kunmap_ops[i], address,
				map->flags | GNTMAP_host_map, -1);
		}
	}

	pr_debug("map %d+%d\n", map->index, map->count);
	err = gnttab_map_refs(map->map_ops, use_ptemod ? map->kmap_ops : NULL,
			map->pages, map->count);
	if (err)
		return err;

	for (i = 0; i < map->count; i++) {
		if (map->map_ops[i].status) {
			err = -EINVAL;
			continue;
		}

		map->unmap_ops[i].handle = map->map_ops[i].handle;
		if (use_ptemod)
			map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
	}
	return err;
}

static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
{
	int i, err = 0;
	struct gntab_unmap_queue_data unmap_data;

	if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
		int pgno = (map->notify.addr >> PAGE_SHIFT);
		if (pgno >= offset && pgno < offset + pages) {
			/* No need for kmap, pages are in lowmem */
			uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno]));
			tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
			map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
		}
	}

	unmap_data.unmap_ops = map->unmap_ops + offset;
	unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
	unmap_data.pages = map->pages + offset;
	unmap_data.count = pages;

	err = gnttab_unmap_refs_sync(&unmap_data);
	if (err)
		return err;

	for (i = 0; i < pages; i++) {
		if (map->unmap_ops[offset+i].status)
			err = -EINVAL;
		pr_debug("unmap handle=%d st=%d\n",
			map->unmap_ops[offset+i].handle,
			map->unmap_ops[offset+i].status);
		map->unmap_ops[offset+i].handle = -1;
	}
	return err;
}

static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
{
	int range, err = 0;

	pr_debug("unmap %d+%d [%d+%d]\n", map->index, map->count, offset, pages);

	/* It is possible the requested range will have a "hole" where we
	 * already unmapped some of the grants. Only unmap valid ranges.
	 */
	while (pages && !err) {
		while (pages && map->unmap_ops[offset].handle == -1) {
			offset++;
			pages--;
		}
		range = 0;
		while (range < pages) {
			if (map->unmap_ops[offset+range].handle == -1) {
				range--;
				break;
			}
			range++;
		}
		err = __unmap_grant_pages(map, offset, range);
		offset += range;
		pages -= range;
	}

	return err;
}

/* ------------------------------------------------------------------ */

static void gntdev_vma_open(struct vm_area_struct *vma)
{
	struct grant_map *map = vma->vm_private_data;

	pr_debug("gntdev_vma_open %p\n", vma);
	atomic_inc(&map->users);
}

static void gntdev_vma_close(struct vm_area_struct *vma)
{
	struct grant_map *map = vma->vm_private_data;
	struct file *file = vma->vm_file;
	struct gntdev_priv *priv = file->private_data;

	pr_debug("gntdev_vma_close %p\n", vma);
	if (use_ptemod) {
		/* It is possible that an mmu notifier could be running
		 * concurrently, so take priv->lock to ensure that the vma won't
		 * vanishing during the unmap_grant_pages call, since we will
		 * spin here until that completes. Such a concurrent call will
		 * not do any unmapping, since that has been done prior to
		 * closing the vma, but it may still iterate the unmap_ops list.
		 */
		mutex_lock(&priv->lock);
		map->vma = NULL;
		mutex_unlock(&priv->lock);
	}
	vma->vm_private_data = NULL;
	gntdev_put_map(priv, map);
}

static struct page *gntdev_vma_find_special_page(struct vm_area_struct *vma,
						 unsigned long addr)
{
	struct grant_map *map = vma->vm_private_data;

	return map->pages[(addr - map->pages_vm_start) >> PAGE_SHIFT];
}

static const struct vm_operations_struct gntdev_vmops = {
	.open = gntdev_vma_open,
	.close = gntdev_vma_close,
	.find_special_page = gntdev_vma_find_special_page,
};

/* ------------------------------------------------------------------ */

static void unmap_if_in_range(struct grant_map *map,
			      unsigned long start, unsigned long end)
{
	unsigned long mstart, mend;
	int err;

	if (!map->vma)
		return;
	if (map->vma->vm_start >= end)
		return;
	if (map->vma->vm_end <= start)
		return;
	mstart = max(start, map->vma->vm_start);
	mend   = min(end,   map->vma->vm_end);
	pr_debug("map %d+%d (%lx %lx), range %lx %lx, mrange %lx %lx\n",
			map->index, map->count,
			map->vma->vm_start, map->vma->vm_end,
			start, end, mstart, mend);
	err = unmap_grant_pages(map,
				(mstart - map->vma->vm_start) >> PAGE_SHIFT,
				(mend - mstart) >> PAGE_SHIFT);
	WARN_ON(err);
}

static void mn_invl_range_start(struct mmu_notifier *mn,
				struct mm_struct *mm,
				unsigned long start, unsigned long end)
{
	struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
	struct grant_map *map;

	mutex_lock(&priv->lock);
	list_for_each_entry(map, &priv->maps, next) {
		unmap_if_in_range(map, start, end);
	}
	list_for_each_entry(map, &priv->freeable_maps, next) {
		unmap_if_in_range(map, start, end);
	}
	mutex_unlock(&priv->lock);
}

static void mn_invl_page(struct mmu_notifier *mn,
			 struct mm_struct *mm,
			 unsigned long address)
{
	mn_invl_range_start(mn, mm, address, address + PAGE_SIZE);
}

static void mn_release(struct mmu_notifier *mn,
		       struct mm_struct *mm)
{
	struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
	struct grant_map *map;
	int err;

	mutex_lock(&priv->lock);
	list_for_each_entry(map, &priv->maps, next) {
		if (!map->vma)
			continue;
		pr_debug("map %d+%d (%lx %lx)\n",
				map->index, map->count,
				map->vma->vm_start, map->vma->vm_end);
		err = unmap_grant_pages(map, /* offset */ 0, map->count);
		WARN_ON(err);
	}
	list_for_each_entry(map, &priv->freeable_maps, next) {
		if (!map->vma)
			continue;
		pr_debug("map %d+%d (%lx %lx)\n",
				map->index, map->count,
				map->vma->vm_start, map->vma->vm_end);
		err = unmap_grant_pages(map, /* offset */ 0, map->count);
		WARN_ON(err);
	}
	mutex_unlock(&priv->lock);
}

static const struct mmu_notifier_ops gntdev_mmu_ops = {
	.release                = mn_release,
	.invalidate_page        = mn_invl_page,
	.invalidate_range_start = mn_invl_range_start,
};

/* ------------------------------------------------------------------ */

static int gntdev_open(struct inode *inode, struct file *flip)
{
	struct gntdev_priv *priv;
	int ret = 0;

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
		return -ENOMEM;

	INIT_LIST_HEAD(&priv->maps);
	INIT_LIST_HEAD(&priv->freeable_maps);
	mutex_init(&priv->lock);

	if (use_ptemod) {
		priv->mm = get_task_mm(current);
		if (!priv->mm) {
			kfree(priv);
			return -ENOMEM;
		}
		priv->mn.ops = &gntdev_mmu_ops;
		ret = mmu_notifier_register(&priv->mn, priv->mm);
		mmput(priv->mm);
	}

	if (ret) {
		kfree(priv);
		return ret;
	}

	flip->private_data = priv;
	pr_debug("priv %p\n", priv);

	return 0;
}

static int gntdev_release(struct inode *inode, struct file *flip)
{
	struct gntdev_priv *priv = flip->private_data;
	struct grant_map *map;

	pr_debug("priv %p\n", priv);

	mutex_lock(&priv->lock);
	while (!list_empty(&priv->maps)) {
		map = list_entry(priv->maps.next, struct grant_map, next);
		list_del(&map->next);
		gntdev_put_map(NULL /* already removed */, map);
	}
	WARN_ON(!list_empty(&priv->freeable_maps));
	mutex_unlock(&priv->lock);

	if (use_ptemod)
		mmu_notifier_unregister(&priv->mn, priv->mm);
	kfree(priv);
	return 0;
}

static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv,
				       struct ioctl_gntdev_map_grant_ref __user *u)
{
	struct ioctl_gntdev_map_grant_ref op;
	struct grant_map *map;
	int err;

	if (copy_from_user(&op, u, sizeof(op)) != 0)
		return -EFAULT;
	pr_debug("priv %p, add %d\n", priv, op.count);
	if (unlikely(op.count <= 0))
		return -EINVAL;

	err = -ENOMEM;
	map = gntdev_alloc_map(priv, op.count);
	if (!map)
		return err;

	if (unlikely(atomic_add_return(op.count, &pages_mapped) > limit)) {
		pr_debug("can't map: over limit\n");
		gntdev_put_map(NULL, map);
		return err;
	}

	if (copy_from_user(map->grants, &u->refs,
			   sizeof(map->grants[0]) * op.count) != 0) {
		gntdev_put_map(NULL, map);
		return -EFAULT;
	}

	mutex_lock(&priv->lock);
	gntdev_add_map(priv, map);
	op.index = map->index << PAGE_SHIFT;
	mutex_unlock(&priv->lock);

	if (copy_to_user(u, &op, sizeof(op)) != 0)
		return -EFAULT;

	return 0;
}

static long gntdev_ioctl_unmap_grant_ref(struct gntdev_priv *priv,
					 struct ioctl_gntdev_unmap_grant_ref __user *u)
{
	struct ioctl_gntdev_unmap_grant_ref op;
	struct grant_map *map;
	int err = -ENOENT;

	if (copy_from_user(&op, u, sizeof(op)) != 0)
		return -EFAULT;
	pr_debug("priv %p, del %d+%d\n", priv, (int)op.index, (int)op.count);

	mutex_lock(&priv->lock);
	map = gntdev_find_map_index(priv, op.index >> PAGE_SHIFT, op.count);
	if (map) {
		list_del(&map->next);
		if (populate_freeable_maps)
			list_add_tail(&map->next, &priv->freeable_maps);
		err = 0;
	}
	mutex_unlock(&priv->lock);
	if (map)
		gntdev_put_map(priv, map);
	return err;
}

static long gntdev_ioctl_get_offset_for_vaddr(struct gntdev_priv *priv,
					      struct ioctl_gntdev_get_offset_for_vaddr __user *u)
{
	struct ioctl_gntdev_get_offset_for_vaddr op;
	struct vm_area_struct *vma;
	struct grant_map *map;
	int rv = -EINVAL;

	if (copy_from_user(&op, u, sizeof(op)) != 0)
		return -EFAULT;
	pr_debug("priv %p, offset for vaddr %lx\n", priv, (unsigned long)op.vaddr);

	down_read(&current->mm->mmap_sem);
	vma = find_vma(current->mm, op.vaddr);
	if (!vma || vma->vm_ops != &gntdev_vmops)
		goto out_unlock;

	map = vma->vm_private_data;
	if (!map)
		goto out_unlock;

	op.offset = map->index << PAGE_SHIFT;
	op.count = map->count;
	rv = 0;

 out_unlock:
	up_read(&current->mm->mmap_sem);

	if (rv == 0 && copy_to_user(u, &op, sizeof(op)) != 0)
		return -EFAULT;
	return rv;
}

static long gntdev_ioctl_notify(struct gntdev_priv *priv, void __user *u)
{
	struct ioctl_gntdev_unmap_notify op;
	struct grant_map *map;
	int rc;
	int out_flags;
	unsigned int out_event;

	if (copy_from_user(&op, u, sizeof(op)))
		return -EFAULT;

	if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT))
		return -EINVAL;

	/* We need to grab a reference to the event channel we are going to use
	 * to send the notify before releasing the reference we may already have
	 * (if someone has called this ioctl twice). This is required so that
	 * it is possible to change the clear_byte part of the notification
	 * without disturbing the event channel part, which may now be the last
	 * reference to that event channel.
	 */
	if (op.action & UNMAP_NOTIFY_SEND_EVENT) {
		if (evtchn_get(op.event_channel_port))
			return -EINVAL;
	}

	out_flags = op.action;
	out_event = op.event_channel_port;

	mutex_lock(&priv->lock);

	list_for_each_entry(map, &priv->maps, next) {
		uint64_t begin = map->index << PAGE_SHIFT;
		uint64_t end = (map->index + map->count) << PAGE_SHIFT;
		if (op.index >= begin && op.index < end)
			goto found;
	}
	rc = -ENOENT;
	goto unlock_out;

 found:
	if ((op.action & UNMAP_NOTIFY_CLEAR_BYTE) &&
			(map->flags & GNTMAP_readonly)) {
		rc = -EINVAL;
		goto unlock_out;
	}

	out_flags = map->notify.flags;
	out_event = map->notify.event;

	map->notify.flags = op.action;
	map->notify.addr = op.index - (map->index << PAGE_SHIFT);
	map->notify.event = op.event_channel_port;

	rc = 0;

 unlock_out:
	mutex_unlock(&priv->lock);

	/* Drop the reference to the event channel we did not save in the map */
	if (out_flags & UNMAP_NOTIFY_SEND_EVENT)
		evtchn_put(out_event);

	return rc;
}

#define GNTDEV_COPY_BATCH 16

struct gntdev_copy_batch {
	struct gnttab_copy ops[GNTDEV_COPY_BATCH];
	struct page *pages[GNTDEV_COPY_BATCH];
	s16 __user *status[GNTDEV_COPY_BATCH];
	unsigned int nr_ops;
	unsigned int nr_pages;
};

static int gntdev_get_page(struct gntdev_copy_batch *batch, void __user *virt,
			   bool writeable, unsigned long *gfn)
{
	unsigned long addr = (unsigned long)virt;
	struct page *page;
	unsigned long xen_pfn;
	int ret;

	ret = get_user_pages_fast(addr, 1, writeable, &page);
	if (ret < 0)
		return ret;

	batch->pages[batch->nr_pages++] = page;

	xen_pfn = page_to_xen_pfn(page) + XEN_PFN_DOWN(addr & ~PAGE_MASK);
	*gfn = pfn_to_gfn(xen_pfn);

	return 0;
}

static void gntdev_put_pages(struct gntdev_copy_batch *batch)
{
	unsigned int i;

	for (i = 0; i < batch->nr_pages; i++)
		put_page(batch->pages[i]);
	batch->nr_pages = 0;
}

static int gntdev_copy(struct gntdev_copy_batch *batch)
{
	unsigned int i;

	gnttab_batch_copy(batch->ops, batch->nr_ops);
	gntdev_put_pages(batch);

	/*
	 * For each completed op, update the status if the op failed
	 * and all previous ops for the segment were successful.
	 */
	for (i = 0; i < batch->nr_ops; i++) {
		s16 status = batch->ops[i].status;
		s16 old_status;

		if (status == GNTST_okay)
			continue;

		if (__get_user(old_status, batch->status[i]))
			return -EFAULT;

		if (old_status != GNTST_okay)
			continue;

		if (__put_user(status, batch->status[i]))
			return -EFAULT;
	}

	batch->nr_ops = 0;
	return 0;
}

static int gntdev_grant_copy_seg(struct gntdev_copy_batch *batch,
				 struct gntdev_grant_copy_segment *seg,
				 s16 __user *status)
{
	uint16_t copied = 0;

	/*
	 * Disallow local -> local copies since there is only space in
	 * batch->pages for one page per-op and this would be a very
	 * expensive memcpy().
	 */
	if (!(seg->flags & (GNTCOPY_source_gref | GNTCOPY_dest_gref)))
		return -EINVAL;

	/* Can't cross page if source/dest is a grant ref. */
	if (seg->flags & GNTCOPY_source_gref) {
		if (seg->source.foreign.offset + seg->len > XEN_PAGE_SIZE)
			return -EINVAL;
	}
	if (seg->flags & GNTCOPY_dest_gref) {
		if (seg->dest.foreign.offset + seg->len > XEN_PAGE_SIZE)
			return -EINVAL;
	}

	if (put_user(GNTST_okay, status))
		return -EFAULT;

	while (copied < seg->len) {
		struct gnttab_copy *op;
		void __user *virt;
		size_t len, off;
		unsigned long gfn;
		int ret;

		if (batch->nr_ops >= GNTDEV_COPY_BATCH) {
			ret = gntdev_copy(batch);
			if (ret < 0)
				return ret;
		}

		len = seg->len - copied;

		op = &batch->ops[batch->nr_ops];
		op->flags = 0;

		if (seg->flags & GNTCOPY_source_gref) {
			op->source.u.ref = seg->source.foreign.ref;
			op->source.domid = seg->source.foreign.domid;
			op->source.offset = seg->source.foreign.offset + copied;
			op->flags |= GNTCOPY_source_gref;
		} else {
			virt = seg->source.virt + copied;
			off = (unsigned long)virt & ~XEN_PAGE_MASK;
			len = min(len, (size_t)XEN_PAGE_SIZE - off);

			ret = gntdev_get_page(batch, virt, false, &gfn);
			if (ret < 0)
				return ret;

			op->source.u.gmfn = gfn;
			op->source.domid = DOMID_SELF;
			op->source.offset = off;
		}

		if (seg->flags & GNTCOPY_dest_gref) {
			op->dest.u.ref = seg->dest.foreign.ref;
			op->dest.domid = seg->dest.foreign.domid;
			op->dest.offset = seg->dest.foreign.offset + copied;
			op->flags |= GNTCOPY_dest_gref;
		} else {
			virt = seg->dest.virt + copied;
			off = (unsigned long)virt & ~XEN_PAGE_MASK;
			len = min(len, (size_t)XEN_PAGE_SIZE - off);

			ret = gntdev_get_page(batch, virt, true, &gfn);
			if (ret < 0)
				return ret;

			op->dest.u.gmfn = gfn;
			op->dest.domid = DOMID_SELF;
			op->dest.offset = off;
		}

		op->len = len;
		copied += len;

		batch->status[batch->nr_ops] = status;
		batch->nr_ops++;
	}

	return 0;
}

static long gntdev_ioctl_grant_copy(struct gntdev_priv *priv, void __user *u)
{
	struct ioctl_gntdev_grant_copy copy;
	struct gntdev_copy_batch batch;
	unsigned int i;
	int ret = 0;

	if (copy_from_user(&copy, u, sizeof(copy)))
		return -EFAULT;

	batch.nr_ops = 0;
	batch.nr_pages = 0;

	for (i = 0; i < copy.count; i++) {
		struct gntdev_grant_copy_segment seg;

		if (copy_from_user(&seg, &copy.segments[i], sizeof(seg))) {
			ret = -EFAULT;
			goto out;
		}

		ret = gntdev_grant_copy_seg(&batch, &seg, &copy.segments[i].status);
		if (ret < 0)
			goto out;

		cond_resched();
	}
	if (batch.nr_ops)
		ret = gntdev_copy(&batch);
	return ret;

  out:
	gntdev_put_pages(&batch);
	return ret;
}

static long gntdev_ioctl(struct file *flip,
			 unsigned int cmd, unsigned long arg)
{
	struct gntdev_priv *priv = flip->private_data;
	void __user *ptr = (void __user *)arg;

	switch (cmd) {
	case IOCTL_GNTDEV_MAP_GRANT_REF:
		return gntdev_ioctl_map_grant_ref(priv, ptr);

	case IOCTL_GNTDEV_UNMAP_GRANT_REF:
		return gntdev_ioctl_unmap_grant_ref(priv, ptr);

	case IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR:
		return gntdev_ioctl_get_offset_for_vaddr(priv, ptr);

	case IOCTL_GNTDEV_SET_UNMAP_NOTIFY:
		return gntdev_ioctl_notify(priv, ptr);

	case IOCTL_GNTDEV_GRANT_COPY:
		return gntdev_ioctl_grant_copy(priv, ptr);

	default:
		pr_debug("priv %p, unknown cmd %x\n", priv, cmd);
		return -ENOIOCTLCMD;
	}

	return 0;
}

static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
{
	struct gntdev_priv *priv = flip->private_data;
	int index = vma->vm_pgoff;
	int count = vma_pages(vma);
	struct grant_map *map;
	int i, err = -EINVAL;

	if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
		return -EINVAL;

	pr_debug("map %d+%d at %lx (pgoff %lx)\n",
			index, count, vma->vm_start, vma->vm_pgoff);

	mutex_lock(&priv->lock);
	map = gntdev_find_map_index(priv, index, count);
	if (!map)
		goto unlock_out;
	if (use_ptemod && map->vma)
		goto unlock_out;
	if (use_ptemod && priv->mm != vma->vm_mm) {
		pr_warn("Huh? Other mm?\n");
		goto unlock_out;
	}

	atomic_inc(&map->users);

	vma->vm_ops = &gntdev_vmops;

	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;

	if (use_ptemod)
		vma->vm_flags |= VM_DONTCOPY;

	vma->vm_private_data = map;

	if (use_ptemod)
		map->vma = vma;

	if (map->flags) {
		if ((vma->vm_flags & VM_WRITE) &&
				(map->flags & GNTMAP_readonly))
			goto out_unlock_put;
	} else {
		map->flags = GNTMAP_host_map;
		if (!(vma->vm_flags & VM_WRITE))
			map->flags |= GNTMAP_readonly;
	}

	mutex_unlock(&priv->lock);

	if (use_ptemod) {
		err = apply_to_page_range(vma->vm_mm, vma->vm_start,
					  vma->vm_end - vma->vm_start,
					  find_grant_ptes, map);
		if (err) {
			pr_warn("find_grant_ptes() failure.\n");
			goto out_put_map;
		}
	}

	err = map_grant_pages(map);
	if (err)
		goto out_put_map;

	if (!use_ptemod) {
		for (i = 0; i < count; i++) {
			err = vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE,
				map->pages[i]);
			if (err)
				goto out_put_map;
		}
	} else {
#ifdef CONFIG_X86
		/*
		 * If the PTEs were not made special by the grant map
		 * hypercall, do so here.
		 *
		 * This is racy since the mapping is already visible
		 * to userspace but userspace should be well-behaved
		 * enough to not touch it until the mmap() call
		 * returns.
		 */
		if (!xen_feature(XENFEAT_gnttab_map_avail_bits)) {
			apply_to_page_range(vma->vm_mm, vma->vm_start,
					    vma->vm_end - vma->vm_start,
					    set_grant_ptes_as_special, NULL);
		}
#endif
		map->pages_vm_start = vma->vm_start;
	}

	return 0;

unlock_out:
	mutex_unlock(&priv->lock);
	return err;

out_unlock_put:
	mutex_unlock(&priv->lock);
out_put_map:
	if (use_ptemod)
		map->vma = NULL;
	gntdev_put_map(priv, map);
	return err;
}

static const struct file_operations gntdev_fops = {
	.owner = THIS_MODULE,
	.open = gntdev_open,
	.release = gntdev_release,
	.mmap = gntdev_mmap,
	.unlocked_ioctl = gntdev_ioctl
};

static struct miscdevice gntdev_miscdev = {
	.minor        = MISC_DYNAMIC_MINOR,
	.name         = "xen/gntdev",
	.fops         = &gntdev_fops,
};

/* ------------------------------------------------------------------ */

static int __init gntdev_init(void)
{
	int err;

	if (!xen_domain())
		return -ENODEV;

	use_ptemod = !xen_feature(XENFEAT_auto_translated_physmap);

	err = misc_register(&gntdev_miscdev);
	if (err != 0) {
		pr_err("Could not register gntdev device\n");
		return err;
	}
	return 0;
}

static void __exit gntdev_exit(void)
{
	misc_deregister(&gntdev_miscdev);
}

module_init(gntdev_init);
module_exit(gntdev_exit);

/* ------------------------------------------------------------------ */